Micro C-4 semiconductor die and method for depositing connection sites thereon

ABSTRACT

A semiconductor die having multiple solder bumps, each having a diameter less than about 100 microns, and the method for making such a die are described. The solder bumps are preferably about 10 microns in diameter, and the pitch between the solder bumps is less than 100 microns, and preferably less than or equal to 10 microns. A thermal solder jet apparatus is utilized to deposit solder material to form the solder bumps. The apparatus includes a print head having a plurality of solder ejection ports. Each ejection port has an associated gas ejection conduit connected to a chamber containing one or more hydride films. The hydride film is heated to disassociate hydrogen gas. The hydrogen gas rapidly builds up in the conduit which leads to the ejection port which is loaded with a solder material and forces the ejection of the solder material from the port. A controller controls and choreographs the movements of the movable substrate and movable drive so as to accurately deposit material in desired locations on the semiconductor dies.

[0001] This is a continuation-in-part of U.S. patent application Ser.No. 09/546,084, the disclosure of which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates generally to semiconductor dies and moreparticularly to forming connection sites on flip chip semiconductordies.

BACKGROUND

[0003] The formation of connection sites on integrated circuits is wellknown. Conventional methods of forming connection sites are described,for example, in U.S. Pat. No. 6,117,299 (Rinne et al.) and U.S. Pat. No.6,074,895 (Dery et al.).

[0004] With the growing complexity and increased numbers of transistorswhich can be placed on a single ULSI chip or die has come additionaldemands on the wiring and connection site processes. The number ofinternal metal layers required to interconnect the newer, more complexmicroprocessors has dramatically increased, as have the number ofexternal connection sites. Due to the increased complexity, lower yieldand added cost associated with the metallurgy, it is desirable tofabricate smaller semiconductor dies and place more wiring levels in thepackaging. To accomplish this without degrading performance, a largenumber of exterior die connection sites are required.

[0005] One of the most efficient and compact ways for providing externaldie connection sites uses solder bumps in the so-called flip chip or C-4(i.e., the Controlled Collapse Chip Connection) process. This technologyeliminates the need to wire bond connections from the die bond pads to apackaging lead frame, and offers more connection sites, higher speeds,improved heat transfer, and can be used with smaller die sizes. AlthoughC-4 technology is somewhat costly in terms of time, materials, andequipment, and although it presents certain environmental issues, theuse of solder bumped integrated circuits is growing at a significantrate. At present, conventional large flip chip semiconductor dies mayprovide hundreds of connection sites.

[0006] The importance of this technology is underscored by the formationof the “MicroFab Consortium” (MicroFab) of private and governmentalentities for the purpose of exploring and developing new methods forapplying solder bumps and other materials to integrated circuit dies,optical circuits, hybrids, chip carriers and other devices. Theliterature suggests that MicroFab has successfully developedmanufacturing prototypes of piezoelectrically actuated print heads forejecting low-melting point solder balls of well-defined sizes at ratesapproaching several kilohertz (kHz). Although piezoelectric-based solderball printers have several attractive characteristics, they are limitedby the fact that piezoelectric device strength decreases rapidly withrising temperatures and vanishes at their Curie temperatures. The Curietemperatures of useful ceramics are well under 300° C. Thus, the abilityto manipulate solder viscosity and surface tension by raisingtemperature is limited in such print heads. Other significantlimitations to using piezoelectric-based print heads includes theircomplexity and the great difficulty in mass producing them in large,inexpensive, relatively light weight arrays.

[0007] Thus, a need exists for a method of forming a micro flip chipwhich contains a very high density of solder bumps, and to do so in away which is not restricted by the Curie temperatures of the print headmaterials.

SUMMARY

[0008] The invention provides a flip chip semiconductor die whichincludes a substrate, a plurality of bond pads located on the substrate,and a plurality of solder bumps deposited on the bond pads. Each of thesolder bumps is less than about 100 microns in diameter and the solderbumps are aligned in rows such that the pitch between solder bumpswithin the same row is less than about 100 microns. In a preferredembodiment, one or both of the solder bump diameter and pitch may beless than or equal to 10 microns.

[0009] The invention further provides a semiconductor device thatincludes a die having one or more a metallurgy layers positioned over asubstrate, an insulating layer deposited on the uppermost metallurgylayer, and a plurality of exterior connection sites. A solder bump isdeposited on each connection site and is less than about 100 microns indiameter, and may be less than or equal to 10 microns.

[0010] The invention also provides a system for depositing solder on aplurality of bond pads located on semiconductor dies. The systemincludes a movable substrate adapted to move at least one semiconductordie back and forth in a first plane, a movable drive including at leastone print head, and a controller for controlling the movements of themovable drive and the movable substrate. The movable drive is adapted tomove the print head back and forth in a second plane and the print headis adapted to deposit a solder bump at the connection sites of thesemiconductor die.

[0011] The invention further provides a print head adapted to depositsolder bumps having a diameter of less than 100 microns, and preferably10 or less microns, and a pitch of less than 100 microns, and preferably10 or less microns. The print head includes pockets of a metallichydride, preferably titanium hydride, within one or more chambers. Theprint head further includes a solder reservoir, a solder conduit, a gasconduit and an ejection port. By passing a current through a heatingelement, the solder in the solder reservoir is melted, allowing it toflow to the ejection port. The metallic hydride pockets are heated to atemperature sufficient to generate hydrogen, which increases thepressure of the hydrogen gas within each chamber and allows ejection ofthe solder from the ejection port.

[0012] These and other advantages and features of the invention will bemore readily understood from the following detailed description of theinvention which is provided in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a partial top view of a flip chip semiconductor dieconstructed in accordance with an embodiment of the invention.

[0014]FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.

[0015]FIG. 3 is a partial cross-sectional view through a channel of asolder-ejecting print head used in forming the semiconductor die of FIG.1.

[0016]FIG. 4 is a partial top-view perspective of the print head of FIG.2.

[0017]FIG. 5 is a cross-sectional view through the print head takenalong line V-V of FIG. 3.

[0018]FIG. 6 is a perspective view of a thermal solder jet system inaccordance with an embodiment of the invention.

[0019]FIG. 7 is a flow diagram of the steps involved in fabricating asemiconductor die in accordance with an embodiment of the invention.

[0020] FIGS. 8-13 illustrate various stages of a semiconductor die beingconstructed in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] FIGS. 1-2 illustrate a flip chip semiconductor die 50 fabricatedaccording to an exemplary embodiment of the invention. The semiconductordie 50 includes a substrate 53 containing fabricated semiconductordevices and features and metallurgy layers, an upper metallurgy layer52, an insulating layer 51, e.g. an oxide layer, and a passivating layer57. A plurality of conductive bond pads 54 are located on the insulatinglayer 51 surrounded by the passivating layer 57. Each bond pad 54 has acorresponding solder bump 56 on a surface thereof, creating a micro C-4ball array 61. The solder bumps 56 are formed of a solder material whichmay contain lead or which may be lead-free.

[0022] A respective via 58 extends from each bond pad 54 through theoxide layer 51 to the upper metallurgy layer 52. Each via 58 is linedwith a conductive material 59, allowing electrical connection betweenthe solder bumps 56 and circuitry on the metallurgy layer 52. Althoughthe illustrated semiconductor die 50 shows the ball array 61 lining theouter edges thereof, it is to be appreciated that the solder bumps 56may be arrayed in rows and/or columns or in any desired pattern acrossan entire surface of the insulating layer 51. Also, although the upperlayers of the die 50 are shown as having one metallurgy layer 52, itshould be understood that the bond pads 54 may be electrically connectedthrough the vias 58 to other metallurgy layers of the die 50 besides theuppermost metallurgy layer 52.

[0023] Conventional semiconductor dies include solder bumps 56 having adiameter of 100 microns or more and a pitch between solder bumps of 100microns or more. The solder bumps 56 of the semiconductor die 50constructed in accordance with the invention have a diameter D of lessthan about 100 microns, and preferably as small as about 10 microns orless. Further, the semiconductor die 50 has a pitch P between solderbumps 56 within the same row or column of less than about 100 microns,and preferably about 10 microns or less. Since the diameter D and thepitch P are each about a magnitude smaller than conventional diametersand pitches, the potential density of connection sites, i.e., the solderbumps 56, on the semiconductor die 50 is greater than the density ofconnection sites on conventional semiconductor dies by about two ordersof magnitude.

[0024] FIGS. 3-5 illustrate a thermal solder jet apparatus capable ofdepositing the solder bumps 56 on the semiconductor die 50 connectionsites with a diameter and/or pitch less than 100 microns. In theillustrated thermal solder jet apparatus, liquid solder is ejected froman array of conduits by a burst of hydrogen gas created by thermallydecomposing a metallic compound such as a titanium hydride (TiH₂) film.

[0025] In the illustrated thermal solder jet apparatus, hydrogen gaspressure bursts are generated by heating small volumes of a metalliccompound, such as titanium hydride (TiH₂), or other similar materials totheir disassociation temperatures (usually on the order of 200 to 800°C.) in a relatively enclosed volume. The temperature at which thehydrogen disassociates from a given film depends on the particularhydride involved. Vanadium hydride begins to decompose at temperaturesof around 200° C. while TiH₂ begins to decompose at around 500 to 600°C. While the precise hydrogen desorption kinetics depends on suchvariables as grain size and oxygen content, it is clear that hydrogenevolves virtually spontaneously from TiH₂ at temperatures betweenapproximately 600 and 700° C. While TiH₂ is preferred as the pressuresource in the embodiment of the invention disclosed herein, other metalhydrides, oxides, and nitrides behave similarly and may also be useful.

[0026] The thermal solder jet apparatus illustrated in FIGS. 3-5includes a print head 10. The print head 10 is normally oriented suchthat a solder ejection port 12 points downward in the direction ofgravity during operation; however, FIGS. 3-5 are drawn at 90 degreesfrom this orientation for clarity. One skilled in the art will recognizethat the print head 10 in an actual manufacturing environment wouldlikely be suspended over an integrated circuit (or other appropriatesubstrate) for ejection of solder (or other appropriate liquid)thereupon. Also, the print head 10 would normally be connected toappropriate drive and control electronics at contact pads 38 (FIG. 4)and to a stepper motor to position the print head 10 to appropriatelocations over the integrated circuit. Moreover, an ambient stream of aninert gas or a surrounding vacuum system is ordinarily used to preventoxidation of the solder during its ejection and to regulate cooling ofthe solder bumps on the integrated circuit. The vacuum may also behelpful in removing spent hydrogen gas from the thermal solder jetapparatus. However, since these details are known to one of skill andare not necessary for understanding the workings of the thermal solderjet apparatus, only the details of the print head 10, and not itssurrounding environment, are discussed in detail.

[0027] The print head 10 includes a transparent substrate 14, preferablyformed of glass, which has a gas conduit 16 and a solder conduit 18etched therein. The print head 10 also includes a wafer 20, preferablyincluding silicon, which has a solder feed-through 22 etched therein.The solder feed-through 22 is in fluid connection with the solderconduit 18. The various structures can be formed on the wafer 20 and thesubstrate 14 by a variety of different well-known processes known in theart of semiconductor fabrication, including the use of wet etching andreactive ion etching. The wafer 20 and the substrate 14 are separatelyprepared with the appropriate structures and then bonded together, forexample, by use of a low melting glass or epoxy, or by Mallory bonding.

[0028] Prior to the bonding of the wafer 20 and the substrate 14, adielectric such as a silicon dioxide layer 25 is formed on the wafer 20.The layer 25 can be either thermally grown or deposited, and may beselectively etched away in unwanted locations if desired. Thereafter, anarray of small islands (or a single large film) of titanium is formed onthe layer 25 by, for example, titanium sputtering and etching. Thetitanium islands are then converted to TiH₂ islands 24 by exposing thetitanium to hydrogen at a temperature of approximately 300 to 500° C. Athydrogen pressures of 0.1 to 1.0 atmospheres, the titanium will beconverted into a hydride within a few tenths of seconds to a couple ofminutes, depending on the specific hydrogenation conditions and thestructural morphology and purity of the titanium. Note that thishydrogenation of the titanium can be accomplished after the wafer 20 isjoined to the substrate 14.

[0029] The space in which a group of TiH₂ islands are found is referredto herein as a chamber 17. Each chamber 17 provides a source of pressurefor a single channel in the print head 10, the channel being thecombination of a chamber 17, the gas conduit 16, the solder conduit 18,the solder flow-through 22, and a solder ejection port 12, as shown incross-section in FIG. 3. In an actual commercial embodiment, the printhead 10 would likely have several channels (three are shown in FIG. 4)so that a row of solder bumps may be printed at one time.

[0030] A solder reservoir 26, which is preferably independently formedof glass, is filled with a sufficient amount of solder 28 to produce adesired number of solder bumps, such as solder bumps 56, on theintegrated circuits, such as the semiconductor die 50, served by theprint head 10. The solder 28 may contain lead or may be lead-freesolder. The solder reservoir 26 may be joined to the wafer 20 in avariety of ways, including the use of a low melting glass or epoxy, orby Mallory bonding. The solder reservoir 26 itself can be formed inseveral ways. One way is to metallurgically cast the solder 28 into ashape that fits the reservoir 26. This cast can then be placed insidethe reservoir 26 before it is joined to the wafer 20. Alternatively, thesolder reservoir 26 can have a cover plate (not shown). In thisembodiment, the main body of the reservoir 26 may be joined to the wafer20 and then the solder cast is added. Then, the cover plate is joined tothe reservoir main body. This joining process, as one of skill in theart would recognize, depends on the melting temperature of the solder 28as well as the temperature needed to accomplish the bonding. The solderreservoir 26 also includes a vent hole 32 to equalize the pressureinside of the reservoir after an amount of solder has been ejected fromthe print head 10.

[0031] After connection of the reservoir 26 to the wafer 20 and duringoperation of the print head 10, a current may be passed through aheating element 30 which is built into or on the wafer 20 between it andthe solder reservoir 26. The heating element 30, which is preferably aresistive heating element, when activated provides a heating temperaturewhich exceeds the melting point of the solder 28 in the solder reservoir26, allowing the solder 28 to flow through the solder feed-through 22into the solder conduit 18 and out of the solder ejection port 12 whenejected. A suitable resistive heating element 30 can be fabricated in anumber of ways, but it is presently preferred to form the heatingelement 30 as a passivated thin film resistor, or a diffused resistorstructure built into the wafer 20. Furthermore, the geometry of theresistive heating element 30 is preferably a single serpentine structureunderlying the entire solder reservoir 26, although this is not shown.The two ends of the resistive heating element 30 can be connected to thecontact pads 38 (FIG. 4) so that current may be passed therethrough byelectronics (not shown) of the print head 10. Additionally, the printhead 10 may include additional temperature sensing and control circuitryto optimize the temperature of solder 28.

[0032] Prior to the interconnection of the wafer 20, the substrate 14,and the solder reservoir 26, portions of the wafer 20 (including thesolder flow-through 22) and the substrate 14 (including the solderconduit 18), and the interior of the solder reservoir 26, are covered bya non-oxidizable metal film. These portions are labeled S₁ in FIG. 3.Such metal films are preferably formed at portions S₁ by variouswell-known processes including physical sputtering and chemical vapordeposition of a suitable non-oxidizable metal, such as platinum,rhodium, palladium, gold and perhaps nickel (which forms only about 10angstroms of tarnishing oxide under clean conditions). The function ofthe non-oxidizable metal film is to treat those surfaces that will be incontact with the molten solder 28 during operation of the print head 10so that the solder 28 wets them. Due to surface tension effects, andassisted by gravity, the molten solder 28 will wet only the surfacescovered by the non-oxidizable metal film. In this manner, the solderconduit 18 will be “self-primed” with solder 28 after each ejectionevent.

[0033] The portions S₂ not coated with the non-oxidizable metal(including the gas conduit 16) are instead coated with athermodynamically stable, clean oxide, such as silicon dioxide, aluminumoxide, etc. These portions are not wetted by the molten solder 28.Optionally, the S₂ portions may be coated by other materials thatcontrol the incursion of other liquids that might be used with thisinvention. A perfluoroalkoxy copolymer, such as a DuPont Teflon® 340PFA, is one such example. This polymer has excellent high-temperatureproperties and the low surface energy characteristic of Teflon®. Whilenot necessary in an application involving the ejection of solder, amaterial such as Teflon® is necessary when ejecting liquids that wetoxides. In any event, the force of gravity tends to keep solder fromflowing upwards by capillary action into the gas conduit 16 and thechamber 17 regardless of the surface treatment of the S₂ portions.

[0034] During operation of the print head 10, a small-spot (e.g.,approximately one square micrometer) laser beam 34 is rastered throughthe substrate 14 and onto the TiH₂ islands 24 to generate hydrogenwithin the chamber 17. This sudden release of hydrogen creates asuitably high pressure of hydrogen gas within the chamber 17 to ejectthe solder 28 in the solder conduit 18 out the solder ejection port 12and onto the integrated circuit below. Cooling fins 36 may be mounted onthe top of wafer 20 to screen from the chamber 17 the excessive heatgenerated by the laser beam 34, thus minimizing the unwanted release ofhydrogen from the TiH₂ islands 24 that are not struck with the laserbeam 34. As an alternative to the laser beam, an array of passivatedthin film resistors or diffused resistors could be formed on or in thewafer 20 to rapidly heat the TiH₂ islands 24 to their decompositiontemperatures. However, in view of the large number of TiH₂ islands 24,the electronics to control the heating of each individual island 24might be unnecessarily complicated when compared with the use of thelaser beam 34.

[0035] The silicon dioxide layer 25 that underlies the TiH₂ islands 24optimizes heat transfer from the laser 34 to the islands 24. The layer25 is less thermally conductive than the underlying wafer 20, and thusserves to sharpen the temperature rise experienced by the TiH₂ islands24 during exposure to laser beam 34. In other words, the layer 25thermally isolates the TiH₂ islands 24 from the other components in thesystem. The thickness of the layer 25 should be thick enough to providea suitably quick temperature rise to the islands 24, but should also bethin enough to allow heat to diffuse from the islands 24 to the coolingfins 36 during the time period between strikes of the laser 34.Preferably, the thickness of the layer 25 may be between about 50 andabout 200 angstroms, as such a thickness would allow for reasonablyrapid cooling, which of the two parameters (quick temperature rise andheat diffusion) is the more important. Finite element analysis may beemployed to optimize the thickness of layer 25. In addition, thelocation at which the laser beam 34 strikes the TiH₂ islands 24 can varyto optimize the cooling of the chamber 17. For example, the laser beam34 can be made to strike an island 24 on the right side of the chamber17, followed by a strike on an island 24 on the left side of the chamber17, etc.

[0036] An example describing several critical parameters is now providedto show the feasibility of printing an array of 80 by 80 solder bumps 56onto the semiconductor die 50, each bump 56 having a diameter D of 40microns, and being separated by a pitch of 100 microns. While thisexample is directed to producing a pitch of about 100 microns,preferably the pitch would be equal to or less than 10 microns. Tomaximize printing speed, the print head 10 should contain 80 solderejection ports 12 (and their related structures) separated at a distanceof 100 microns from each other to deposit solder bumps 56 at a pitch of100 microns. Obviously, for a pitch of equal to or less than 10 microns,the solder ejection ports 12 are to be separated at a distance of equalto or less than 10 microns.

[0037] A hemispherical solder bump 56 that is 40 microns in diameter Dis equivalent to a cylindrical volume which is 40 microns in diameterand 13.3 microns in length. Alternatively, a solder cylinder 53.2microns in length by 20 microns in diameter yields a solder bump of thesame volume. This assumes, of course, that surface tension forces aresufficient during the time of flight to significantly reshape theelongated projectile to a relatively rounded one or alternatively thatreshaping would take place mainly on the substrate. Assuming that thesolder 28 is predominantly composed of lead, and thus has a density ofapproximately 10 g/cm³, the mass of the solder bump 56 is approximately2.67×10⁻⁸ g, or 5.88×10⁻¹¹ lbs. Neglecting surface energy effects in thesolder conduit 18, the steady-state pressure required to support thatmass in a solder conduit 18 that is 40 micrometers in diameter isextremely small, approximately 3.0×10⁻⁵ lbs/in² or 2.0×10⁻⁶ atmospheres.

[0038] To deposit the solder bumps 56 with a pitch P of 100 microns, areasonably sized chamber 17 is needed. Such a chamber 17 can include acontinuous TiH₂ film or an array of TiH₂ islands 24 as shown in FIG. 4.With a chamber of this size, twenty thousand, TiH₂ islands 24 one squaremicrometer in area can be fabricated for each chamber 17, assuming thatthe TiH₂ film covers only twenty-five percent of the available chamberarea for any given channel.

[0039] Table 1 below provides estimates of the maximal hydrogenpressures that are achievable for various sizes of chambers 17 and TiH₂islands 24. In making these estimates, it was assumed that all of thehydrogen is released from the indicated TiH₂ island. The hydrogenpressure is assumed to rise stepwise in this temporarily closed volumein a time (probably less than several microseconds) that is too short torealize solder ejection from the solder ejection port 12. As oneexample, a 1 by 1 by 3 cubic micrometer TiH₂ island 24 containsapproximately 5.39×10⁻⁹ cm³ of hydrogen at 25° C. and one atmosphere. Ifthe space between the cover plate and the top of the TiH₂ film is set atone micrometer and the TiH₂ film is assumed to be continuous (notpatterned into islands), the hydrogen pressure buildup within the spacein the 100 by 800 by 1 cubic micrometer (8×10⁻⁸ cm³) chamber 17 will beapproximately 0.07 atmospheres, or one psi. The pressure required tosupport the mass of a 40 micrometer diameter bump in a 40 micrometerdiameter solder conduit 18 was estimated to be only 3.0×10⁻⁵ psi. Theforce generated by the hydrogen release in this case is therefore over30,000 times greater than that needed to support the mass of the solder28. Indeed, in each of the examples provided in Table 1, the estimatedhydrogen pressure is at least a few orders of magnitude greater than theestimated pressure needed to support the mass of solder 28, suggestingthat the disclosed thermal solder jet apparatus operates as desired toeffectuate suitable ejection of the solder 28 out of the solder ejectionport 12 to create the solder bumps 56 on the semiconductor die 50.

[0040] Unlike the piezoelectric print heads of conventional apparatus,the disclosed embodiments can be made to function at higher temperaturesif it is desirable to increase the ejection velocity. The diffusivity ofhydrogen in titanium coupled with the relative thinness of the TiH₂sources indicates that the hydrogen can be released in less than amicrosecond, provided the hydride temperature can be raised just asrapidly to values on the order of approximately 700 to 800° C.Notwithstanding these physical observations, the fact that the chamberpressure is a few orders of magnitude greater than that necessary tosupport the solder mass (as discussed in the last paragraph) suggeststhat the ejection velocity of any of the embodiments disclosed in Table1 will be sufficient.

[0041] It is essential to remove at least part of the hydrogen insidethe chamber 17 after the solder 28 is ejected. Otherwise the solderconduit 18 cannot be primed anew with fresh solder 28 via capillaryaction. Since the capillary forces are quite strong, however, it isprobably only necessary to reduce the hydrogen pressure in the chamber17 to a value that is perhaps one or two orders of magnitude below themaximum ejection pressure. In this regard, estimates were made of thetime required for hydrogen removal assuming that the print head 10 wasoperating in a vacuum ambient. For the purpose of this estimation, thehydrogen outflow through the channel can be treated as a viscous gasflow through a cylindrical tube. Assume that this tube is 40 micrometersin diameter by 80 micrometers in length, the conductance of air isapproximately 53×10⁻³ CM³/sec through a tube of these dimensions at 25°C., and the conductance of hydrogen is about twice this value. Factoringin such parameters as the average mean free path allows one to determinethe time to evacuate a chamber from atmospheric pressure to varioussmaller values. For the small volume (about 8×10⁻⁸ CM³) of the chamberdisclosed, a conductance of about 53×10⁻³ CM³/sec is sufficient to lowerthe pressure in the chamber 17 from 10⁶ to 10⁵ microns of mercury inabout 6.3×10⁻⁷ seconds. An additional 6.3×10⁻⁶ seconds will lower thepressure by yet another order of magnitude.

[0042] Thus, it is estimated that the solder conduit 18 will be refilledwith solder 28 in perhaps 10 to 20 microseconds. This is an improvementover thermal ink jet print heads of the same dimension, which take lessthan a millisecond to refill. However, if it is conservatively assumedthat the disclosed embodiment will take one millisecond to refill, anygiven channel in the disclosed print head 10 could operate at anejection rate of about 10³ Hz. Thus, it would take about 80 millisecondsto print an integrated circuit with an array of 80 by 80 solder bumps.Since the number of TiH₂ islands 24 in each channel can vary fromroughly 10,000 to 40,000, a print head built in accordance with thedisclosed embodiment should be able to print between 125 to 500integrated circuits. TABLE 1 ESTIMATED CHAMBER PRESSURES FOR VARIOUSGEOMETRIES Releasable Chamber H₂ Chamber Chamber Free Vol. TiH₂ VolumePress. Area Ht. (cm³) Area Ht. (cm³) atm psi 100 × 800 1 8 × 10⁻⁸ 1 35.46 × 10⁻⁹ 0.068 1.0 100 × 800 5 40 × 10⁻⁸  1 3 5.46 × 10⁻⁹ 0.014 0.2100 × 400 1 4 × 10⁻⁸ 2 5 1.82 × 10⁻⁸ 0.46 6.70 100 × 100 5 5 × 10⁻⁸ 9 101.64 × 10⁻⁷ 3.3 48.2  100 × 10³  10  1 × 10⁻⁸ 9 10 1.64 × 10⁻⁷ 0.16 2.4

[0043] The Chamber and TiH₂ heights are in micrometers, while the H₂volumes are at standard temperature and pressure, or 60° F. and 14.7psia. The Chamber height refers to the distance between the top of thehydride and the cover plate.

[0044]FIG. 6 illustrates a system for depositing the solder bumps 56 ona plurality of semiconductor dies 50. As shown in FIG. 6, a plurality ofprint heads 10 may be mounted on a movable drive, such as a rotatingshaft 60, to allow movement of the print heads 10 in a direction X.Additionally, semiconductor dies 50 may be positioned upon a movablesubstrate 65 so that they may be moved in a direction Y underneath theprint heads 10. Both the shaft 60 and the movable substrate 65 areconnected with a controller 70 which controls and choreographs themovements of the dies 50 and the print heads 10 in order to accuratelydeposit solder bumps 56 on the dies 50. By linking multiple print heads10 together, several steps can be done serially at each bond pad 54. Forexample, a first print head 10 may be filled with a cleaning agent, andduring its pass over the dies 50 it ejects small drops of the cleaningagent to remove unwanted tarnishing surface oxides. A second print head10 may include adhesive metal or alloy, which it ejects on each of thebond pads 54. A third print head 10, which includes the bumpingmetallurgy, such as the solder 28, ejects the solder 28 on the bond pads54 to create the solder bumps 56. Alternatively, if larger connectionsites are desired, multiple passes of the third print head 10 canincrease the size of the solder bumps 56. And finally, a fourth printhead 10 may include a passivation material which is suitable to preventor retard the growth of tarnishing oxides which may grow during storageof the dies 50.

[0045] Instead of having each linked print head 10 depositing differentmaterials, any number of or all of the linked print heads 10 may depositthe same material. Further, successive print heads 10 may each deposit asingle element which, when combined with the other deposited elements,forms the solder bumps 56.

[0046] Furthermore, the controller 70 may control the actions of themovable substrate 65 and the shaft 60 such that the placement of solderbumps 56 may be personalized from die 50 to die 50 and across a singledie 50. Additionally, since the thermal solder jet apparatus may beoperated under a curtain of inert gas, deposition of the solder bumps 56may be accomplished at a lower cost, since a vacuum system is notrequired. Also, the thermal solder jet apparatus is relativelyinexpensive and is relatively highly reliable, both factors of whichwill further lessen production costs.

[0047] A method of producing a semiconductor die 50 having an array ofsolder bumps 56 will next be described with reference to FIGS. 7-13. Theprocess begins with the fabrication of the uppermost metallurgy layer 52of the die 50. At step 100, the metallurgy layer 52 including circuitryis deposited on the substrate 53 (FIGS. 7-8). An oxide layer 51 is thendeposited on the metallurgy layer 52 at step 110 (FIGS. 7, 9). In apreferred embodiment, the oxide layer 51 is chemical vapor deposited onthe metallurgy layer 52 and then planerized through chemical mechanicalpolishing. The vias 58 are then etched in the oxide layer 51 at step120. Preferably, a resist layer is deposited over the oxide layer and avia hole pattern is developed in the resist layer, allowing accurateetching of the vias 58. At step 130, the bond pads 54 and any surfacecircuitry are patterned and deposited (FIGS. 7, 10-11). Preferably, aresist layer 80 is deposited on the oxide layer 51 and patterns for thesurface circuitry and the bond pads 54 are exposed. The resist ispatterned to expose the surface circuitry, leaving resist where no metalis desired. Then, metal is deposited in the pattern. In a preferredembodiment, the metal deposited in a pattern within the oxide layer 51includes a metallurgical stack of 500 angstroms of zirconium, followedby 750 angstroms of nickel, 5,000 angstroms of copper, and 750 angstromsof gold. This level of metallurgy provides both a last wiring level andis the pad limiting metallurgy. Any unwanted metal may be lifted offusing a tape liftoff. The remaining resist layer 80 is removed. Then, atstep 140 a polymer material 57, preferably a polyimide, is spun on theoxide layer 51 and over the bond pads 54 and cured (FIGS. 7, 12). Thepolyimide serves as a passivation layer, or an insulator. This isfollowed with the deposition of a photoresist material 84 which isimaged at the bond pads 54. The photoresist material 84 is developed andthe image is transferred through the photoresist material 84 and thepolyimide material 57 using appropriate RIE processes. Then thephotoresist material 84 is stripped.

[0048] After printing the bond pad pattern, at step 150 the bond pads 54are pre-cleaned (FIG. 7). Specifically, a print head 10 which is filledwith a cleaning agent passes over the dies 50 and ejects small drops ofthe cleaning agent to remove unwanted tarnishing surface oxides. Then,if required, at step 160 an adhesive metal is deposited on the bond pads54. For example, if solder 28 formed of a lead-tin composition isdeposited on bond pads 54 formed of gold, no adhesive material would berequired. This may be accomplished by passing another print head 10having the adhesive metal or alloy over the bond pads 54. Then, yetanother print head 10, which includes the bumping metallurgy, such asthe solder 28, is passed over the bond pads 54 at step 170, ejecting thesolder 28 on the bond pads 54 to create the solder bumps 56. Finally, afourth print head 10 may be passed over the dies 50 to eject apassivation material onto the solder bumps 56 at step 180. Thepassivation material prevents or retards the growth of tarnishing oxideswhich may grow during storage of the dies 50. After step 180, the dies50 which are still part of a wafer can be diced and flipped onto anappropriate substrate.

[0049] while the invention has been described in detail in connectionwith exemplary embodiments known at the time, it should be readilyunderstood that the invention is not limited to such disclosedembodiments. Rather, the invention can be modified to incorporate anynumber of variations, alterations, substitutions or equivalentarrangements not heretofore described, but which are commensurate withthe spirit and scope of the invention. For example, while a thermalsolder jet apparatus is described as being used to produce the flip chipsemiconductor dies of the invention, it should be appreciated that theinvention is not limited to being produced by such an apparatus.Accordingly, the invention is not to be seen as limited by the foregoingdescription, but is only limited by the scope of the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A flip chip semiconductor die, comprising: aplurality of exterior bond pads formed on said die; and a plurality ofsolder bumps deposited on said bond pads, wherein each said solder bumpis less than about 100 microns in diameter.
 2. The semiconductor die ofclaim 1, wherein said solder bumps are about 10 microns or less indiameter.
 3. The semiconductor die of claim 1, wherein at least some ofsaid solder bumps are spaced by a pitch of less than about 100 microns.4. The semiconductor die of claim 3, wherein said pitch is about 10microns or less.
 5. The semiconductor die of claim 1, wherein saidsolder bumps are attached to each said bond pad with an adhesive metal.6. A semiconductor device, comprising: a substrate; a die having ametallurgy layer positioned over said substrate; an oxide layerdeposited over said metallurgy layer; and a plurality of connectionsites coupled to said metallurgy layer through said oxide layer, whereina solder bump deposited on each said connection site is less than about100 microns in diameter.
 7. The packaged semiconductor device of claim6, wherein said solder bumps are about 10 microns or less in diameter.8. The packaged semiconductor device of claim 6, wherein at least someof said solder bumps are spaced by a pitch of less than about 100microns.
 9. The packaged semiconductor device of claim 8, wherein saidpitch is about 10 microns or less.
 10. The packaged semiconductor deviceof claim 6, wherein said solder bumps are attached to each saidconnection sites with an adhesive metal.
 11. A system for depositingsolder on a plurality of connection sites located on semiconductor dies,said system comprising: a movable substrate adapted to move at least onesemiconductor die in a first plane; a movable drive including at leastone print head, said movable drive adapted to move said print head in asecond plane, said print head adapted to deposit on the semiconductordie a material having a diameter of less than about 100 microns; and acontroller for controlling the movements of said movable drive and saidmovable substrate.
 12. The system of claim 11, wherein said movablesubstrate is adapted to move back and forth in said first plane.
 13. Thesystem of claim 11, wherein said movable drive is adapted to move saidprint head back and forth in said second plane.
 14. The system of claim11, wherein said movable drive is a rotatable shaft.
 15. The system ofclaim 14, wherein at least four print heads are mounted on saidrotatable shaft.
 16. The system of claim 15, wherein at least two ofsaid print heads deposit the same material.
 17. The system of claim 16,wherein each said print head deposits a different material.
 18. Thesystem of claim 17, wherein a first of said print heads deposits apre-cleaning solution.
 19. The system of claim 18, wherein a second ofsaid print heads deposits an adhesive metal.
 20. The system of claim 19,wherein a third of said print heads deposits a solder material.
 21. Thesystem of claim 20, wherein said solder material contains lead.
 22. Thesystem of claim 20, wherein said solder material is lead-free.
 23. Thesystem of claim 20, wherein a fourth of said print heads deposits apassivation material.
 24. The system of claim 11, wherein said printhead deposits a solder material on said semiconductor die in multipleconnection sites, each said connection site being spaced by a pitch ofless than about 100 microns.
 25. The system of claim 24, wherein eachsaid connection site is spaced by a pitch of about 10 microns or less.26. The system of claim 11, wherein said print head deposits a soldermaterial on said semiconductor die on at least one connection site, saiddeposited solder material having a diameter of less than about 100microns.
 27. The system of claim 26, wherein said deposited soldermaterial has a diameter of about 10 microns or less.
 28. A print headfor ejecting a solder material, comprising: a chamber including ametallic compound which generates a gas when heated; a reservoirincluding the solder material; a channel in communication with saidchamber and said reservoir; an ejection port in communication with saidchannel, wherein a pressure increase due to the generation of the gas insaid chamber causes said solder material to be ejected from saidejection port, said print head being configured to eject said soldermaterial from said ejection port in such a way as to create a depositionof said solder material that has a diameter of less than about 100microns.
 29. The print head of claim 28, wherein said print head isconfigured to eject said solder material in such a way as to create adeposition of said solder material that has a diameter of about 10microns or less.
 30. The print head of claim 28, wherein said print headincludes multiple ejection ports, each said ejection port so located asto eject said solder material in such a way as to deposit said soldermaterial in a plurality of locations spaced by a pitch of less thanabout 100 microns.
 31. The print head of claim 30, wherein each saidlocations are spaced by a pitch of about 10 microns or less.
 32. Theprint head of claim 28, wherein said metallic compound is a metallichydride.
 33. The print head of claim 32, wherein said metallic hydridecomprises titanium hydride.
 34. The print head of claim 28, furthercomprising a laser, wherein said laser heats said metallic compound togenerate said gas.
 35. A method of fabricating a flip chip semiconductordie, comprising depositing a solder material on each of a plurality ofconnection sites, wherein the diameter of each said deposited soldermaterial is less than about 100 microns.
 36. The method of claim 35,wherein said deposition of solder material is accomplished with a singleprint head.
 37. The method of claim 35, wherein said depositioncomprises: depositing a first element from a print head; and depositingat least a second element from a print head, wherein the combination ofthe elements forms the solder material.
 38. The method of claim 35,wherein said deposition comprises depositing the solder material fromtwo or more print heads.
 39. The method of claim 35, wherein saiddeposition is accomplished with a plurality of print heads.
 40. Themethod of claim 35, further comprising pre-cleaning the bond pads priorto said deposition of the solder material.
 41. The method of claim 40,further comprising depositing an adhesive metal between saidpre-cleaning and said depositing of the solder material.
 42. The methodof claim 41, further comprising adding a passivation material onto thedeposited solder material.
 43. The method of claim 35, wherein saiddeposition comprises depositing the solder material multiple times at asingle location.